So imagine you and your friend are playing with your toys. You have a really cool toy that your friend wants to play with, but they don't have any toys that you really want to play with. So you say "I'll let you play with my toy, but you have to give me a cookie in return."
That's kind of like quid pro quo. It means "you scratch my back and I'll scratch yours." It's when one person agrees to do something for someone else, but only if the other person agrees to do something specific in return.
But it's important to remember that quid pro quo isn't always a good thing. If someone says "I'll give you this job, but only if you do something for me that you don't feel comfortable with," that's not okay. In those cases, it's important to speak up and say no.